Telephone system



Nov. 12, 1940. F. PFLEIDERER ETAL 2,221,652

TELEPHONE SYSTEM Filed Oct. 13, 1 937 2 Sheets-Sheet l INVENTOR. FRITZPFLEIDEREP F RT BY v BERNHARD SEIF E I ATTORNEY;

1940. F. PFLEIDERER EI'AL 2,221,552

TELEPHONE SYSTEM Filed Oct. 15, 19:57

2 Sheets-Sheet 2 INVENTOR. FRIT z PFLEIDERER ERNHARD sEIFFERT ATTORNEY.

Patented Nov. 12, 1940 TELEPHONE SYSTEM Fritz Pfleiderer,Berlin-Wilmersdorf, and Bernhard Seificrt, Berlin-Charlottenburg,Germany, assignors to Siemens & Halske Aktiengesellschaft, Wernerwerk,Siemensstadt, near Berlin,

Germany Application October 13, 1937, Serial No. 168,836

1 In Germany October 14, 1936 3 Claims.

The subject of the invention is a circuit arrangement for remotecommunication systems and in particular telephone systems, which servesthe purpose of selectively blocking or permitting 5 the transmission ofalternating currents, and in particular speech currents, over a lineduring the establishment or during the existence of a call at a desiredstage of the call.

This is achieved in that dry-plate rectifiers are arranged in the remotecommunication line and block the line as regards the transmission ofalternating currents such as for example speech currents or release itin dependence upon the mode of their connection to the leads of the line(series or shunt connection) and in dependence upon whether they aretraversed by direct current or not.

It is known in pay station telephones for example to prevent speechcurrents passing from the calling subscriber to the called subscriberbefore the former has paid the full fee for the call. This is effectedby devices at the pay station or in the exchange for example by blockingthe microphone by means of valves and in other ways.

In systems with speech amplifiers and in loud speaker systems so-called'echo suppressors are known which forexample when sending speech blockthe receiving circuit and when receiving block the sending circuit inorder to prevent the known echo and back coupling efiects. These devicesconsist for the most part of thermionic tubes which efiect the blockingin one or other speech direction by relaysdisposed in their anodecircuits.

Moreover, in systems having lines equipped with amplifiers devices areknown'which serve to allow the signal receiving means provided at theamplifiers of the individual sections of the line only to respond toalternating currents in a particular direction this being effected forexample by bridge circuits andin other ways.

The arrangement according to the invention is differentiated from theseknown arrangements by the manner in which the blocking or release of thelines for the flow of speech currents is efiected. This mode ofachieving the desired result differs from the known arrangements onaccount of its great simplicity, considerable greater efiiciency andsmaller production and maintenance cost.

The invention will now be described in greater detail with reference tothe embodiments shown in the drawings. The embodiment according to Figs.1-2 shows the application of the principle of the invention to a paystation system and Fig. 3 shows the application to a loudspeaker system.Fig. 4 shows the resistance characteristic of a rectifier.

The direct current J flowing through the rectifier is represented by theabscissae and the ordinates represent the corresponding impedance R.Only those devices which are necessary to enable the invention to beunderstood are represented and described.

The possibilities of the application of the invention are not limited tothe embodiments shown but may be used also ior various other purposesarising in remote communication systems and telephone systems such asfor example the temporary coupling and differential influencing ofimpulse repeaters, registers and the like.

In the embodiment according to Fig. 1 it is assumed that of the speechcurrents transmitted to the subscribers connected to the two lines LIand L2 only that from subscriber T2 can pass unimpeded to subscriber Tlwhile the transmission of speech currents proceeding from subscriber TIto subscriber T2 is normally blocked. Subscriber Tl may be assumed to bethe calling party and calls from the pay station while subscriber T2calls from a normal subscribers station. The calling subscriber Tl willbe prevented, so long as he has not paid the full fee, i. e., has notinserted it in the pay station collecting device (not shown), fromconversing with the called subscriber. So long as he has not paid thefull fee he can hear the called party as soon as the latter replies buthis own speech is not transmitted to the called party. Y g I For thispurpose metal dry-plate rectifiers are incorporated in the leads of theline in the exchange as a blocking means. The dry-plate rectifierspossess a high resistancev to the speech currents i. e., weakalternating currents but whena direct current which is relatively largeinpro-' portion to the amplitude of the alternating current traversesthe rectifier the resistance of the latter is reduced by a certainamount as is indicated in Fig. 4 and increases again immediately to itshigh value when the direct current flow ceases.

In Fig. 1 the rectifiers are represented by GI and G2. So long as nodirect current flows through them, i. e., in the normal condition, theyblock the passage of speech currents from the one subscriber to theother over the lines LI and L2 in both directions. In order now toenable the calling subscriber to know whether his call has beencompleted to the called party he must hear the speech of the calledparty when the latter replies and therefore the blocking of the calledparties speech must be removed.

This is done in the following way: On the side of the blockingrectifiers GI and G2 nearest to the called subscriber a device isarranged which consists of a full wave rectifier GI and for example oidry-plate rectifiers arranged in a fourarmed bridge and an arrangementof coils or a filter circuit Spl and has its input side (alternatingcurrent circuit) connected over a repeater Ue to the leads of the lineand is connected over its output side (direct current circuit) directlyfor example by conductive connection, to the leads of the line. of thecalled subscriber T2 from the line L2 passes to the full wave rectifierG1 is here rectified and the rectified speech current passes over thefilter circuit Spl, lead a blocking rectifier Gl, choke coil Dr,blocking rectifier G2 and back through the filter circuit Spl to thefull wave rectifier Gl. As soon as this direct current flows through theblocking rectifiers GI and G2 their resistance sinks to a low value andthe speech currents can pass unimpeded to the subscriber TI. It may bementioned here that if it is desired still further to increase theblocking effect of the blocking rectifiers a further blocking elementcan be arranged in the direct current path as indicated in Figs. 1 and4. The filter circuit SpZ allows direct current to pass throughunimpeded but not alternating current. As soon as the calling subscriberTI hears the called subscriber T2 who has replied he pays the requisitefee.

In a way which is not shown and which does not concern the presentinvention, a relay, for

example (not shown) is energized and at its contacts Ir and 2a: shuntsthe blocking rectifiers GI and G2 so that subscribers now can conversetogether easily. At contacts 3:12, 4:0, 50: and 6:1: the full waverectifier GZ is disconnected for the remainder of the call. At the endof the call the relay releases again and its contacts Ia: to 60:,inclusive, reassume their normal position. Since the dry-platerectifiers possess no mechanical parts they operate completely withoutinertia so that all the operations take place rapidly and without anydelay. If the rectifier G1 is disposed on the other side of the blockingrectifiers GI and G2 the speech currents passing from the direction LIwould be able to pass to L2 while the speech currents coming from L2would at first be blocked.

The embodiment according to Fig. 2 is difierent from that in Fig. 1 onlyin that the input of the full wave rectifier GZ' i. e., its couplingtransformer Ue' is not directly connected to the line but is inductivelycoupled to it by means of the choke-coil DH, and the output passes overthe point of symmetry between the choke-coils D71 and Dr simultaneouslyover both leads of the line. Since in this embodiment the samereferences are used as in Fig. l the operation may be understood fromthe description and drawing of the latter embodiment.

Part of the incoming speech the line L is situated a similar subscribersstation.

In such systems the acoustic coupling i. e., the distortion produced bythe effect of the sound waves proceeding from the loud speaker on themicrophone must be prevented. This is realized in that the blockingrectifiers are arranged in the branch circuit for transmitting outgoingspeech currents. In this branch is disposed the blocking rectifier GI.So long as no direct current flows over the rectifier the speakingcurrents are prevented from passing over the repeater Ueg in the line Lto the distant subscriber on account of the high resistance of therectifier and the consequent high attenuation of this branch of theline. In order now to permit the uninterrupted flow of the speechcurrents completely automatically and without any operation on the partof the subscriber a portion of the speech currents is led ofi over awinding 3 of the transformer Ue2 and is impressed on the grid of theamplifying tube V2 and is there amplified. These amplified speechcurrents are passed by means of the repeater Ue3 to a full waverectifier GZI for example comprising a network of dry-plate rectifiers,are rectified and are led through the blocking rectifier GI in theoutgoing branch I and through the rectifier G2 in the incoming branch IIof the speaking circuit. A direct current circuit is thus set up whichpasses from the rectifier GZI out over the chokecoils Dr3 and DH theblocking rectifier GI, the choke coil D12 and the blocking rectifier G2and back to the rectifier GZI. On account of the direct current fiow thehigh resistance of the blocking rectifier GI is brought to a low valueand the high attenuation in the branch circuit I is reduced so that thespeech currents pass unimpeded through this circuit and over thetransformer Ueg of the line L and to the subscriber disposed at theother end of the line.

The transformer Ueg and the balancing element N are so arranged as toprevent speech currents from the branch circuit I passing into thebranch for incoming speech currents 11 instead of to the line L andsimilarly to prevent the speech currents incoming over the line Lpassing to the outgoing branch circuit I instead of into the branchcircuit II for incoming speech currents. Since the balancing effect ofthese devices, the transformer and the balancing element are not alwayscompletely effective special care must be taken in the present circuiton account of the high amplification to prevent the outgoing as well asincoming speech currents passing to the output point over thetransformer Ucg. Since direct current is also flowing over the blockingrectifier G2 the impedance of this rectifier to the speech currents isalso reduced to a low value. The reduction of the impedance in theincoming branch circuit produced at the blocking rectifier G2 incontradistinction to the blocking rectifier GI does not, however,produce movable parts operate as a relay having no inertia, theoperations described take place ex ceptionally rapidly and without anydelay.

When now the subscriber Tl ceases to talk and the subscriber at theother end of the line L talks his speech currents incoming over the lineL must be prevented from passing into the outgoing branch I instead ofinto the incoming branch II. When the subscriber Tl ceases to talk, thedirect current flow from the rectifier GZ! over the blocking rectifiersGI and G2 also ceases immediately and these blocking rectifiers oncemore offer their high resistance to the speech current. Since theblocking rectifier G2 is arranged in shunt across the leads of thebranch circuit II its resistance does not constitute any attenuation asregards the speech currents incoming to the branch circuit from the lineL. The speech currents can, therefore, pass unimpeded over thetransformer U64 and the transformer U66 to the grid of the amplifyingtube V4. They are here amplified and operate on the loud speaker L. Aportion of these incoming speech currents are led off over winding 3' ofthe transformer Ue l and are impressed on the grid of the amplifyingtube V3 and are here amplified and are passed over the transformer Uefito the full wave rectifier G13. The direct current fiow produced is ledto the grid of the microphone amplifier VI to constitute a negative gridbias and thereby blocks this amplifier. The microphone M can no longerbe influenced by the waves produced by the loud speaker L and theoscillations incoming to it are prevented from passing into the outgoingbranch circuit I.

The attenuation networks formed by the blocking rectifiers in thecircuit-microphone,

outgoing branch of the circuit, incoming branch of the circuit, loudspeaker and back to the microphoneare so chosen and arranged that thespeech currents passing for example from the outgoing branch of thecircuit are no longer able to operate the loud speaker. The speechcurrents proceeding from the line L from the distant subscriber can,however, overcome the attenuation produced by the blocking rectifier G2when traversed by the direct current so that the distant subscriber isable to break in to the conversation. This is true also for the oppositedirection and the rectifier Gl. In this case also while the distantsubscriber is still speaking the subscriber Tl can take over the lead inthe conversation. His speech currents then overbalance the grid bias ofthe tube VI produced by the additional negative grid potential from G13.

There is, therefore, no need for either of the a subscribers to waituntil the other subscriber which are led off and rectified by therectifiers.

G21 and G12 are also used to eifect an equalization of these variationsin amplitude.

When subscriber Tl for example speaks, the direct current produced bythe rectifier G1 I does not only pass over the blocking rectifiers GIand G2 but also over a further blocking rectifier G3 arranged betweenthe transformers Uel and Ue2 in the outgoing branch I and since this isarranged as a bridge between the leadsof the branch I brings about anincreased attenuation of this circuit on account of the reduction of itshigh resistance so that the speech currents proceeding from themicrophone are reduced in strength. On account of this reduction instrength, however, the direct current fiow is'also reduced in therectifier GZ! by the blocking rectifier G3 and the direct current in therectifier Gll can increase again. This variation abouta normal conditionequalizes the variations in the sound intensity.

The same is true for the speech currents received over the line L fromthe distant subscriber. These are led oil over the transformer Ue5 to afurther full wave rectifier G22 and here influence the blockingrectifier G4 arranged as a bridge across the leads of the branch circuit11. The function of this latter rectifier is the same and brings aboutthe same effect as the blocking rectifier G3 in the outgoing branch I.Thus variations in the sound intensity of the outgoing and incomingspeech currents are equalized so as to insure a uniform transmission ofthe speech even in the case of varying attenuation in the line and otherun-uniform conditions in the transmitting system.

What is claimed is:

1. In combination, a circuit for the transmission of speech currents, avolume control rectifier bridging the input end of said circuit andnormally having an impedance of such value as to present substantiallyno blocking to incoming speech currents, a series connected rectifier inthe output end of said circuit normally having an impedance of suchvalue as to substantially block outgoing speech currents, voicecontrolled means responsive to speech currents at a point insaid circuitintermediate to said two rectifiers and effective to cause both of saidrectifiers to be traversed by direct current thereby to decrease theirimpedance, the blocking of the input end of said circuit increasing andthe blocking of the output end decreasing responsive to a decrease inthe impedance of the corresponding rectifiers.

2. In combination, a circuit for the transmission of speech currents inone direction, a second circuit for the transmission of speech currentsin another direction, a volume control rectifier bridging the input endof said first circuit and normally having an impedance of such value asto present substantially no blocking to incoming speech currents, aseries connected rectifier in the output end of said first circuitnormally having an impedance of such value as to substantially blockoutgoing speech currents, a rectifier bridging the input end of saidsecond circuit and normally having an impedance of such value as topresent substantially no blocking to incoming speech currents, voicecontrolled means responsive to speech currents at a point in said firstcircuit intermediate said first two rectifiers and effective to causeall three of said rectifiers to be traversed by direct current therebyto decrease their impedance, the blocking of the input ends of both ofsaid circiuts increasing and the blocking of the output end of saidfirst circuit decreasing responsive to a decrease in the impedance 0 thecorresponding rectifiers. 3. In combination, a circuit for thetransmission of speech currents in one direction, a second circuit forthe transmission of speech currents in another direction, a volumecontrol rectifier bridging the input end of said first circuit andnormally having an impedance of such value as to present substantiallyno blocking to incoming speech currents, a series connected rectifier'inthe output end of said first circuit normally having an impedance ofsuch value as to substantially block outgoing speech currents, arectifier bridging the input end of said second circuit and normallyhaving an impedance of such Value as to present substantially noblocking to incoming speech currents, voice controlled means responsiveto speech currents at a point in said first circuit intermediate saidfirst two rectifiers and effective to cause all three of said rectifiersto be traversed by direct current thereby to decrease their impedance,the blocking of the input ends of both of said circuits increasing andthe blocking of the output end of said first circuit decreasingresponsive to a decrease in the impedance of the correspondingrectifiers, and voice controlled means responsive to speech currentspassing said rectifier in said second circuit for at times preventingspeech currents from being impressed upon the input end of said firstcircuit.

FRITZ PFIEIDE'RER. BERNI-IARD SEIFFERT.

